This has been happening from a while back when I accelerate hard in first gear, then shift into 2nd, I hear and feel a grinding noise even if the clutch is pressed all the way down. It only happens sometimes. The other few times Ive done this it shifts fine. Could it be the synchros? I know Im pressing down the clutch so it isn't like Im not pressing enough to disengage. If I shift under hard acceleration on any of the other gears 2-3, 3-4, 4-5 it shifts fine with no grinding sound like 1st to 2nd does sometimes.

 

S4? S5? Na? Turbo?
Either way these transmissions are at least 25 years old so......... yeah
Throw some redline or royal purple oil and hope for the best or find another trans but again they are all old.

 

S5 na. Ive heard really good things about Redline but Ive never seen them in person.

 

Well the s5 na trans I had went in the trash. It grinded 2 to 3 but input shaft bearing is what killed it... If it just grinds every once and a while like I said just put some good gear oil in and squeeze some more life out of it...when it goes up grade to a turbo trans.